In our living environment, there are a large number of malodorous molecules having different polarization characteristics and molecular weights. Hitherto, a variety of methods have been developed for reducing various malodorous molecules. Generally, the methods for reducing malodors are broadly classified into a biological method, a chemical method, a physical method, or a sensory method. Among malodorous molecules, short-chain fatty acids and amines, having high polarity, can be reduced through a chemical method; i.e., neutralization. Sulfur-containing compounds such as thiol can be reduced through a physical method; i.e., adsorption. However, there still remain many malodorous molecules, such as medium-chain and long-chain fatty acids and skatole, which cannot be reduced through known malodor reducing techniques.
In mammals including humans, the mechanism for odorant recognition includes binding odorant molecules to olfactory receptors present on olfactory sensory neurons included in the olfactory epithelium, which is present in an upper portion of the nasal cavity, and transmitting the response of the receptors to the central nervous system. It has been reported that, 387 different olfactory receptors are present in human, and the genes encoding these olfactory receptors account for about 3% of the human genome.
Generally, a plurality of olfactory receptors responds to a plurality of odorant molecules. Specifically, one single olfactory receptor responds to a plurality of structurally similar odorant molecules at different affinities, while one single odorant molecule is detected by a plurality of olfactory receptors. It is also reported that a certain odorant molecule which can activate one olfactory receptor serves as an antagonist that inhibits activation of another olfactory receptor. Such combined response of these olfactory receptors leads to recognition of each odor.
Therefore, even in the case where the same odor molecules are present, if other odor molecules exist simultaneously, the receptor response may be inhibited by the other odor molecules, and the odor that is eventually perceived may come out to be completely different. Such a mechanism is referred to as the antagonism of olfactory receptors. Modification of an odor by this antagonism of receptors can specifically cause loss of the perception of a malodor, unlike the deodorization methods involving addition of another odor such as the odor of a perfume or an aromatizing agent. Furthermore, there is no chance of occurrence of any unpleasant feelings caused by the odor of the aromatizing agent.
In regard to nonanoic acid, hexanoic acid, isovaleric acid and the like, which are representative causative substances for body odor, their odors have been hitherto disodorized or deodorized by techniques such as the use of a disodorizer or a deodorizer, and the use of a fragrance or an aromatizing agent (Patent Documents 1 and 2, and Non-Patent Document 1). However, these techniques are methods intended to reduce the initial generation of an odorous substance or to make another odor to be more strongly perceived, and these methods differ from the deodorization by masking based on the antagonism of olfactory sensors. Furthermore, in the conventional methods, when a deodorizer is used, since some time is required to reduce the odorous substance, the methods lack immediate effectiveness. When an aromatizing agent is used, there are occasions in which unpleasant feelings may occur due to the odor of the aromatizing agent itself. In other cases, the conventional methods may even eliminate odors other than an intended malodor. If deodorization by masking based on the antagonism of olfactory receptors is utilized, there is a possibility that the problems described above may be solved.
In order to utilize the antagonism of olfactory receptors, there is a need for a search and identification of substances which exhibit olfactory receptor antagonistic action against individual malodor molecules; however, it is not easy to conduct such a search. Conventionally, the evaluation of an odor has been carried out by a sensory test conducted by experts. However, a sensory test has problems such as a need to foster experts who are capable of evaluating odors, and the characteristic of low throughput.
In order to achieve odor control by utilizing the antagonism of olfactory receptors, it would be an important matter to correlate an odor and an olfactory receptor. In relation to the olfactory receptors that receive nonanoic acid or hexanoic acid, it has been hitherto reported that OR2W1 responds to hexanoic acid and nonanoic acid, OR51E1 responds to nonanoic acid, and OR51L1 responds to hexanoic acid (Non-Patent Document 2). It has also been reported that OR51E1 responds to isovaleric acid (Non-Patent Document 3).
Aldehyde-based fragrance components have been traditionally incorporated into aromatizing/deodorizing agents cleaning compositions and the like for personal care or environment, (Patent Documents 1 to 3). However, these components are used as aromatizing components, and have not been used as antagonists that control the response of olfactory receptors to malodors.